In an optical network, it may be necessary to provide 3R relay partway along an optical transmission path, in consideration of deterioration and loss in the fiber, and crosstalk. FIG. 87 shows a conventional optical network configuration. In order to provide 3R relay, 3R repeaters 1002 are inserted into each optical node device 1001 provided partway along an optical transmission path. In practice, since transmission is possible up to a certain distance without 3R relay, a 3R repeater 1002 is not necessarily provided in every optical node device 1001. However, since the distance over which transmission is possible without 3R relay differs depending on the performance of optical devices contained in the optical node device, the material of the optical fiber between the optical node devices, and the wavelengths used, the distance cannot be determined uniformly, and there is no efficient method of obtaining the distance over which transmission is possible without 3R relay over a whole optical network. Conventionally, as shown in FIG. 87, a 3R repeater 1002 is inserted into each stage so that deterioration of an optical signal can be compensated regardless of the route through which a path is established (for example, refer to non-patent documents 1, 2 and 3).
Non-patent document 1: Eiji Oki, Daisaku Shimazaki, Kohei Shiomoto, Nobaki Matsuura, Wataru Imajuku, and Naoaki Yamanaka, “Performance Evaluation of Distributed-Controlled Dynamic Wavelength-Conversion GMPLS Networks”, Technical report of IEICE, The Institute of Electronics, Information and Communication Engineers, February 2002, pp. 5-10.
Non-patent document 2: Ken-ichi Sato, Naoaki Yamanaka, Yoshihiro Takigawa, Masafumi Koga, Satoru Okamoto, Kohei Shiomoto, Eiji Oki, and Wataru Imajuku, “GMPLS-Based Photonic Multilayer Router (Hikari Router) Architecture: An Overview of Traffic Engineering and Signaling Technology”, IEEE Communications Magazine, March 2002, pp. 96-101.
Non-patent document 3: Eiji Oki, Daisaku Shimazaki, Kohei Shiomoto, Nobuaki Matsuura, Wataru Imajuku, and Naoaki Yamanaka, “Performance of Distributed-Controlled Dynamic Wavelength-Conversion GMPLS Networks”, First International Conference on Optical Communications and Networks 2002, Nov. 11-14, 2002, Shangri-La Hotel, Singapore.
3R repeaters are expensive, so if the use of 3R repeaters is avoided as much as possible, optical networks can be realized extremely economically. However, conventionally, there is no effective method of obtaining the distance over which transmission is possible without 3R relay over a whole optical network. Hence it is not possible to determine the places where 3R repeaters do not need to be provided.
Furthermore, conventionally, in each optical node device, 3R relays are provided in all optical paths passing through the concerned optical node device. Therefore, 3R repeaters are needed to provide 3R relay capability in a large number of optical paths at the same time, and it is difficult to achieve low cost.